A bumper beam for absorbing impact caused at the time of collision is provided on an inner side of a bumper to be provided at a front end of an automobile.
A bumper beam includes a bumper reinforcement to be arranged along a vehicle width direction and a pair of right and left crash boxes (shock absorbing members) which support the bumper reinforcement to a vehicle structure. At the time of collision, the crash box is compressively deformed in an axial direction thereof to thereby absorb the impact energy.
Such a crash box is constituted by a hollow aluminum extruded member, etc., and the outer peripheral wall is formed into a circular shape, a polygonal shape, etc. Further, to improve the absorbing characteristics of impact energy, a crash box in which a plurality of ribs are formed on an inside of the outer peripheral wall is proposed.
The crash box as shown in Patent Document 1, for example, includes an outer peripheral wall hexagonal in cross-section and 6 ribs radially extending from a central axis to an intermediate position of each side portion of the outer peripheral wall. When the crash box receives a compressive load, the crash box repeatedly deforms (buckling-deforms) in the axial direction in an accordion manner while deforming the portion of the outer peripheral wall sandwiched by adjacent nodes convexly and concavely in a radial direction, with the rib connection point and the vertex of the outer peripheral wall as a node and an anti-node, respectively.